Circuit switches

[Bhootnike]

Wanted to confirm my understanding.

Consider two circuits, A and B.
A goes: cell - switch - resistor- back to cell.
B goes: cell- resistor - switch-  back to cell.

A is a safer circuit to have because if we have a closed circuit for both A and B and i plug in 6V cell, the current will happily flow around and around in both. But if then for some reason, the current flowing increases to amounts where it could potentially fry the resistor, e.g. if lightning struck, then circuit A will allow for the resistor to be safe, because there is a switch which can be opened to prevent current reaching resistor.
B on the other hand would mean that even if you opened the switch, and so break the circuit, the current will flow through resistor before reaching open switch and so the resistor will fry.

Correct? or incorrect?

n.b - this is all for understanding purposes, ofc one would not know when to exactly turn switch off!

[Stick]

The most important reason switches are placed before circuit elements is so that the circuit can be broken before any electricity reaches any elements. If this is not the case, damage may occur to the elements and there may be a risk of electrocution. Remember that in the household, switches are also placed in the active line and before any current can access a particular appliance.

Woah, maybe I'm not bad at Physics after all... :S

[Bhootnike]

But if you intend to have the switch open (i.e circuit broken at any given point), it doesnt matter where you put the switch relative to circuit element,
Because if you had the switch at the start, of course no current can flow through the rest of the circuit, but also if you had switch after circuit element, and the switch was open, then no current can flow out of that element because it has nowhere to go, and therefore no current can flow into the element, thus implying that no current can flow out of cell and hence no current can flow into cell.
So either way, no current will reach the resistor?


I am glad you mentioned that in your post, because that is what i got confused about :p

[Stick]

Yes, in this case a switch can only act as a precautionary measure. In household appliances though, a switch and fuse is placed in series before any circuit elements so if there is a short-circuit, the fuse will break the current towards any elements and the switch will divert the electricity into the earth wire and into the ground. If it was afterwards, the increased energy would in fact flow through the circuit elements before it was even broken. In your context, it would make very little difference, but it's always just that little bit safer to put the switch before the resistor.

[Bhootnike]

ok, my understanding has been confirmed, thank you very much stick  

[Stick]

You're welcome. It was good revision for me, because my Unit 1 AOS 2 electricity test is coming up. ^_^